//Sunday, November 15 2009
#include <string>
#include <vector>
#include <map>
#include <queue>
#include <sstream>
#include <algorithm>
// TCHS Single Round Match 57 > Round 1
using namespace std;

typedef long long LL;

class TwoLotteryGames
{
public:
	double getHigherChanceGame(int n, int m, int k)
	{
		LL t = 0;
		for(int i=k; i<=m; i++)
		{
			t+= bm(m,i) * bm(n-m,m-i);
		}
		return double(t) / double(bm(n,m));
	}
	LL sl(int l)
	{
		LL i = 1;
		for(int j=1; j<=l; j++)
			i *= j;
		return i;
	}
	LL bm(int n, int k)
	{
		return sl(n)/(sl(k)*(sl(n-k)));
	}
};
